Study On OFET Nonvolatile Memory Utilizing Bimetal Nanoparticles As Nano-floating-gate

In the past decades, organic electronics have attracted much attention as a hot research topic with the developments of organic semiconductor materials. Significant advances have been made in organic electronic components, such as organic light-emitting diodes (OLEDs), organic solar cells (OSCs), organic field-effect transistors (OFETs) and OFET based nonvolatile memories. Due to the simple fabrication process, low cost, light weight, large area and flexibility, OFETs and OFET nonvolatile memories show a great potential in the application field of panel display, radio-frequency identification tags, smart cards, sensor arrays and so on. A lot of organic semiconductors have a close performance to amorphous silicon in terms of field-effect mobility and some other physical properties, which provides more possibility to realize their widespread use.OFET based nonvolatile memory has been a promising contender as a basic unit of flexible memory in the future, which owns the merits of nondestructive reading, reliable data storage and compatibility with logic circuit architecture. To realize memory effect, it usually uses a chargeable layer to modulate the channel conductivity in OFET nonvolatile memories. And there are three main approaches to modulate and maintain the channel conductivity:(1) retainable polarization of a ferroelectric gate dielectric; (2) charge trapping into a polymeric gate electret; and (3) charge trapping into a floating-gate. Compared with traditional continuous floating-gate, nano-floating-gate has discrete charge trapping sites which benefit to suppressing the charge lateral movements, thus improving the data storage reliability of the OFET nonvolatile memories.Metals possess a relatively large range of work functions and a large number of occupied and unoccupied states around Fermi level, which is of benefit to charge storage. Besides, the size and density of metal nanoparticles (NPs) are easily controlled during preparation. Hence, they are preferred to be utilized as nano-floating-gate in OFET nonvolatile memories for charge trapping. As the typical representatives of common low work function metal and high work function metal, silver (Ag) and platinum (Pt) NPs have been appropriately employed as nano-floating-gate to investigate the influence of metal work function on the performance of OFET nonvolatile memories.In this thesis, we first analyzed the influence of work function of NPs in the floating-gate on the memory performance by fabricating the OFET nonvolatile memories utilizing Ag NPs and Pt NPs as the nano-floating-gate, respectively. It is observed that the Ag NPs floating-gate OFET nonvolatile memory shows a larger negative threshold voltage shift and a smaller positive threshold voltage shift, while the Pt NPs device exhibits an opposite tendency. Thereafter, we fabricated an OFET nonvolatile memory using Ag-Pt bimetal NPs as the floating-gate and the synergistic memory effect was observed in this device. The device shows a larger positive threshold voltage shift and a larger negative threshold voltage shift simultaneously. Thus, a large memory window has been obtained, which appeals to high performance OFET nonvolatile memory applications. Based on the experimental results, we explained the synergistic effect by building a physical model-work function change induced by the surface dipole enhancement. Finally, the model was further verified by the electronic structure characterizations.The work of this thesis, including the NP work function dependent memory performance and the bimetal NPs floating-gate based memory, provides valuable information for designing high performance OFET nonvolatile memories.